Swift By Deya

A reserved word is a word that cannot be used as an identifier, this is a syntactic definition, as mentioned before in Swift Lexical Structure, all lists below are written alphabetically.

• Keywords used in declarations: 

Reserved Word	Details
associatedtype	Associated types are a powerful way of making protocols generic, it gives a placeholder name to a type that’s used as part of the protocol.
class	One of swift’s general purpose, flexible constructs also see struct
deinit	A method that gets automatically called when an object is freed up from memory by ARC.
enum	Enums let’s you define a custom kind of value in Swift, with predefined possible values.
extension	Extensions add new functionality to an existing class, structure, enumeration, or protocol type.
fileprivate	One of swift’s access modifiers.
func	Used for creating functions.
import	A declaration used for importing modules and submodules
init	as per swift documentation, “Initialization is the process of preparing an instance of a class, structure, or enumeration for use.”
inout	inout allows parameters to be changed outside of the function scope.
internal	One of swift’s access modifiers.
let	A keyword used for declaring a constant
open	One of swift’s access modifiers.
operator	A special symbol/ phrase that you use to check, change, or combine values.
private	One of swift’s access modifiers.
precedencegroup	defining precedence groups to use for our custom operators.
protocol	as per swift’s official documentation “A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.”
public	One of swift’s access modifiers.
rethrows	rethrows keyword is used with function that accepts a throwing function as a parameter.
static	defines a static scope.
struct	complex value-types.
subscript	Subscripts allow you to write shortcuts to elements from collections, Sequences in classes, structures and enumerations.
typealias	Defines an alias for an existing type.
var	A keyword used for declaring a variable.

• Keywords used in statements:

Reserved Word	Details
break	One of the control transfer statements, ends execution of a loop, an if statement, or a switch statement.
case	Used for pattern testing.
catch	Used for handling any potential errors caused by a function that throws.
continue	One of the control transfer statements, ends execution of the current iteration of a loop statement but does not stop execution of the loop statement.
default	Used for default cases in switch.
defer	Used for making a block to execute just before a function exits.
do	Used for creating do blocks, for example (do-while, do-catch)
else	Used for executing a block when a condition is not satisfied.
fallthrough	One of the control transfer statements
for	Used for iterating over a sequence.
guard	Used in control transfer statement and optional unwrapping.
if	Used for condition evaluation.
in	In is a keyword defined in the Swift closure syntax as a separator between the function type and the function body in a closure, and used in checking if an object is in a sequence.
repeat	A control flow statement, similar to while loop
return	One of the control transfer statements
throw	Used for throwing an error in a function that throws.
switch	A switch statement considers a value and compares it against several possible matching patterns.
where	Used to filter out values, in statements like switch, for, protocol extension, first, contains, initializers.
while	A control flow statement, it performs a set of statements until a condition becomes false

• Keywords used in expressions and types:

Reserved Word	Details
Any	Any can represent an instance of any type at all, including function types.
as	Used for type casting.
catch	Used in error handling, when an error is thrown, it’s matched against the catch clauses.
false	A literal used to express booleans.
is	Used to check whether an object is of a certain class type
nil	A valueless state that could be assigned to optionals.
rethrows	allows forwarding a thrown error by a given function parameter
self	“self” refers to the current object within a class or struct.
Self	Refers to a type – usually the current type in the current context.
super	super is used to call up to your superclass.
throw	Used for throwing an error in a function that throws.
throws	To mark a function throwing.
true	A literal used to express booleans.
try	The try keyword is used to indicate that a method can throw an error. To catch and handle an error, the throwing method call needs to be wrapped in a do-catch statement.

• Keywords used in patterns: 

Reserved Word
_
.

• Keywords that begin with a number sign (#), literals expressions: 

Reserved Word	Details
#available	Used to determine the availability of APIs at runtime
#colorLiteral	Used to make the XCode IDE to display a color swatch 🟥
#column	column number of the line where it is being run.
#dsohandle	–
#elseif	Literal conditional statement
#else	Literal else statement.
#endif	Literal marker for closing an a literal if statement
#error	Creates a red compiler error & prevents code from compiling
#fileID	Generates concise file string in all language modes.
#fileLiteral	Used to make the XCode IDE link to a local file.
#filePath	Outputs the file path of in which code is being run.
#file	Outputs the name of the file in which code is being run.
#function	Outputs the name of the function where code belongs.
#if	Literal if statement.
#imageLiteral	Used to make the XCode IDE to display an image.
#keyPath	–
#line	line number where it is being run.
#selector	–
#sourceLocation	–
#warning	will cause Xcode to display a warning with the given message.

• Keywords reserved in particular contexts: 

Reserved Word	Details
associativity	defines how operators of the same precedence are grouped together.
convenience	Convenience modifier placed before the init keyword.
didSet	A property observer
dynamic	A declaration modifier used to make use of Objective-C’s dynamism.
final	One of Swift’s access modifiers.
get	Used when getting a computed property.
indirect	Used for recursive Enums
infix	Used when creating custom operators.
lazy	Used for just-in-time calculation.
left	Used to specify the associativity of a custom operator
mutating	Functions marked as mutating can change any property within its enclosing value
none	Used to specify the associativity of a custom operator
nonmutating	–
optional	–
override	Used for overriding child classes.
postfix	Used in creating custom functions, it’s mathematical notation in which operators follow operands.
precedence	Operator precedence is a set of rules that determine which operator is executed before another.
prefix	Used in creating custom functions, it’s mathematical notation in which operators follow operands.
Protocol	A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.
required	Required keyword means that inheriting classes must provide an implementation of the method.
right	Used to specify the associativity of a custom operator
set	Used when getting a computed property.
some	denotes an opaque type.
Type	A metatype type refers to the type of any type, including class types, structure types, enumeration types, and protocol types.
unowned	A reference type, used for memory management.
weak	A reference type, used for memory management.
willSet	A property observer

• Outside the context in which they appear in the grammar, they can be used as identifiers.

The following tokens are reserved as punctuation and can’t be used as custom operators: 

(, )	{, }	[, ]
.	,	:
;	=	@
#	& (as a prefix operator)	->
`	?	! (as a postfix operator)

Obj-C development dates back to 1980s, Swift came with a lot of significant improvements in clarity, performance, safety, and more.

1- Swift is easier to read and maintain

Swift drops legacy conventions, using semicolons to end lines are not needed, also parenthesis are not needed around (conditional expressions), no bracket hell needed for method calls, two-file requirement is dropped by swift, the LLVM compiler can figure out dependencies automatically…

for example, swift adopts modern programming language features like concatenation of two strings together with a “+” operator, along with string interpolation which makes things easier and safer, instead of memorizing special tokens  (%s, %d, %@), that can be a source of crashes!

2- Swift is more safe, and have better memory management

in Obj-C nothing happens if you call a method with a nil pointer variable, not crashing may look like a benefit, but actually this is a source of bugs and unexpected behavior, optional types in swift solves this problem, this means any bug will be fixed sooner or avoided at all in swift code.

In contrast to swift, in Objective-C, ARC is not available for procedural C and other APIs like CoreGraphcis, swift saves the developer brain power for better things, like writing the app’s main logic, instead of handling memory management.

3- Swift is faster, and is less prone to name collisions

A lot of people made benchmarks, concluding swift being faster and more performant than Obj-C.

Obj-C lacked name-spacing, to overcome this issue, a common practice was using a few letters as a prefix, for example NSArray (after NextStep, a company by Steve Jobs), or NSString, … etc.

In swift, namespaces are based on the target that a file relies in, for example, both apple frameworks and google frameworks can have a file called Authentication.swift

4- Swift Supports Dynamic libraries

Obj-C only support static libraries, this is a big downside, swift support dynamic libraries, that can be loaded into the app’s memory directly, this reduces the app total size, and reduces the load time of (on demand) new content.

5- Swift is open-source and has bigger community
Swift has a big community that are actively contributing, hence open-source, it started running in other environments like linux. for example of swift outside of the apple ecosystem, see vapor,  a web framework for Swift.

The Swift language is developed in the open, and all technical or administrative topics about the language or community processes should be directed to the Swift public forums. Public conversations are encouraged, and active developers of the Swift language should monitor the relevant forum categories.

Swift.org